Inkjet printing is a popular and versatile form of print imaging. The Assignee has developed printers that eject ink through MEMS printhead IC's. These printhead IC's (integrated circuits) are formed using lithographic etching and deposition techniques used for semiconductor fabrication.
The micro-scale nozzle structures in MEMS printhead IC's allow a high nozzle density (nozzles per unit of IC surface area), high print resolutions, low power consumption, self cooling operation and therefore high print speeds. Such printheads are described in detail in U.S. Ser. No. 10/160,273 filed Jun. 4, 2002 and U.S. Ser. No. 10/728,804 filed on Dec. 8, 2003 to the present Assignee. The disclosures of these documents are incorporated herein by reference.
The small nozzle structures and high nozzle densities can create difficulties with nozzle clogging, de-priming, nozzle drying (decap), color mixing, nozzle flooding, bubble contamination in the ink stream and so on. Each of these issues can produce artifacts that are detrimental to the print quality. The component parts of the printer are designed to minimize the risk that these problems will occur. The optimum situation would be printer components whose inherent function is able to preclude these problem issues from arising. In reality, the many different types of operating conditions, and mishaps or unduly rough handling during transport or day to day operation, make it impossible to address the above problems via the ‘passive’ control of component design, material selection and so on.
To address this, the Applicant has developed printers with active control of the fluidic systems. These active fluidic systems are described in co-pending application Ser. Nos. 11/482,982; 11/482,983; 11/482,984; 11/495,818; 11/495,819; 11/677,049; 11/677,050; 11/677,051, the contents of which are incorporated by cross reference. While these systems provide the user with the ability to actively manage the static and dynamic fluid conditions throughout the printer, it has been found that the active components within a printer are responsible for a large proportion of the ink borne contaminants. Pumps in particular are prone to shedding particles into the ink flow which can be detrimental to the operation of the nozzles. The wear and friction of surfaces acting against each other eventually generate particle which are directly entrained in the ink flow. Many of the above referenced fluidic designs use peristaltic pumps which introduce additional problems. The flexible tubing within the pump can eventually crack and leak, the tubing loses elasticity and no longer returns to a fully open condition, and the pump has a high torque requirement because of the need to compress the tubing enough to form a seal. To meet the torque requirements, the pump needs to be relatively large which is counter a compact form factor for the printer as a whole.
Ink borne contaminants can be removed with a filter upstream of the printhead. However, the particle size requires the filter pore size to be very small. To maintain the ink flow rate required by a high speed, pagewidth printhead, the filter surface area needs to be impractically large and precludes the compactness required by market expectations.